Antenna system



Dec. 13, 1938, I r J. STERBA N I 2,140,145

' I Q ANTENNA SYSTEM Filed Aug. 16, 1955 FIG. 1,4 I 7%, F/GZA ix ae J: ov M 6 2 L, :1

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a a DEGREES FROM NORMAL LOW sou/cc: By 1 RADIO Z- mews/var 24 SOURCEATTOLWE Patented Dec. 13, 1938 UNITED STATES PATENT OFFEE ANTENNA SYSTEMApplication August 16, 1935, Serial No. 36,446

Claims.

This invention relates to antenna systems and more particularly to adirective antenna system.

An object of this invention is to obtain essentially horizontallypolarized radiations from an antenna array.

.Another object of this invention is to provide a closed circuit forremoving sleet on all elements of an antenna array.

A more particular object of this invention is to increase the eificiencyin theradio transmission and reception of horizontally polarized wavesin a horizontal direction.

Since Heinrich Hertz in 1887 and 1888 constructed the first directiveantenna, radio communication in all its phases has been markedlyimproved. In radio communication between two fixed stations, one mostimportant factor from the economic standpoint is the utilization ofpower of a transmission station to the best advantage. Keeping in stridewith the constant march of improvements in other branches of the radiocommunication art, directive antenna systems have been developed which,in addition to being more effective than the parabolic antenna of Hertz,are far more economical of construction. In some of these systems aninclined or bent wire radiates a component of desired polarization andan undesired component with a polarization normal to; that of thedesired component. To achieve conservation of power and to eliminatefurther fading and distortion, the substantial elimination of radiationof the undesired polarization is essential.

In accordance with this invention, an antenna system emits horizontallypolarized wave components. The antenna system comprises a pair of zigzagradiating elements vertically arranged. Each element is reversely bentat approximately each half wave-length and is oppositely bent from theother element. The corresponding apices of the angles of zigzag elementsare in the same horizontal plane. Non-radiating means supplies radiofrequency power to the elements. The horizontally polarized componentsof the waves radiated from the elements are in phase, while the verticalcomponents of the waves are substantially eliminated in all directions.A directly excited rear curtain having the same configuration as thesystem is also preferably employed in point-to-point radio transmissionand reception.

A more comprehensive understanding of this invention is obtained byreference to the accompanying drawing in which:

Fig. 1 shows diagrammatically a zigzag antenna well known in the art;

Fig. 1A is a diagram of the polarized wave components emitted by part ofthe antenna of the type shown in Fig. 1;

Fig. 2 is a simple antenna constructed in accordance with thisinvention;

Fig. 2A shows diagrammatically the polarized wave component radiated bypart of the system shown in Fig. 2;

Fig. 3 is a modification of the antenna system shown in Fig. 2;

Fig. 4 showsa broadside unidirectional antenna system and transmissionsystem for interconnecting the panels comprising the system; and

Fig. 5 is a polar diagram in a horizontal plane of the directionalcharacteristics of the system shown in Fig. 4.

In Fig. 1 a zigzag type of antenna is represented by the solid linesABCDE. The antenna ABCDE is reversely bent at points B and C and D. Eachof the sections AB, BC, CD and DE is of approximately one-halfwave-length. Radio frequency current is supplied to the antenna ABCDEthrough a transformer 2 from a line I. The dotted curve ABCDE and thearrows indicate the relative current amplitude and direction of thestanding waves along the antenna. At any instant adjacent sections ofthe antenna such as AB and BC are energized by current flowing inopposite directions. Due to the mutual reactance of the conductors inthe several sections, the Wire length along the section is noticeablydifferent than one-half wave-length depending upon the manner in whichthe wire is bent. The exact length which approximates one-halfwavelength is determined empirically by methods wellknown in the art.One method of ascertaining the exact length is described in a paperentitled Theoretical and practical aspects of directional transmittingsystems by E. J. Sterba published in the Proceedings of the Institute ofRadio Engineers, July 1931, vol. 19, No. '7, pp. 1184 to In Fig. 1A,thepolarized wave components of the sections CD and DE are indicated byarrows. The arrows dc and dc indicate the relative current directions ofthe sections DE and DC, re-

spectively. These currents may be resolved into vertical components devand dcv and into horizontal components den and dCh. Since the verticalcurrent components are in opposite directions, the radiations due to thecomponents substantially neutralize each other normal to the paper uponwhich the drawing appears, whereas the radiations from each of theelements due to the horizontal components substantially aid each otherin a horizontal direction. Accordingly, the components of the fieldradiated by DE and DC in a horizontal direction assist each other andresult in a more concentrated emanation of signal energy. Although theundesirable vertical wave components are neutralized at a point in theplane normal to the paper, the vertical polarized wave components arenot neutralized in all directions. For example, the vertical polarizedcomponents do not cancel in the direction ACE. The radiations from DCincur a phase lag in traveling the mean distance between DC and that ofDE. As a result, the greatest efficiency for horizontally polarizedtransmission by the substantial reduction of the vertical polarized wavecomponent is not obtained by the the system shown in Fig. 1.

Fig. 2 shows a directive antenna system for the emission of horizontallypolarized wave components with the substantial reduction of the verticalwave components in all directions. The antenna comprises two elementsrepresented in the drawing by the solid line FGMIK and FGM'IK. Each ofthe elements FGMIK and FG'MI'K is reversely bent at the points G, M, Iand G, M, I, respectively. The sections FG, GM, MI, IK, FG, GM, MI, andIK are approximately one-half wave-length. Due to the mutual reactanceof the several sections, the wire length along each section is notexactly one-half wave-length but approximates that length. The'exactlength of each element is determined empirically by methods wellknown inthe art. The points FF are in a horizontal plane parallel to the ground.The corresponding apices of the angles of the two zigzag elements andincluding the pairs of points GG, MM, II and KK are each in horizontalplanes parallel to the ground and parallel to that containing the pointsFF. Energy is supplied to the two elements FGMIK and FG'MI'K by means ofa line 3 and non-radiating elements FK and FK'. In order to secureproper phasing in the antenna sections or half wave elements, the linesFK and FK' are each made equal in length to an even multiple of a halfwave length since, as illustrated on the drawing, the zigzag antennasFGMIK and FG'M'I'K' are each an even multiple of a half wave-length longand the extremities of each antenna, F and K of antenna FGMIK and F andK of antenna FGMIK, are connected to the same terminal of the radiofrequency source. The relative amplitudes and directions of the currentssupplied by the line 3 to the antenna elements are indicated by thedotted curves and arrows shown in Fig. 2. At any instant adjacentsections of each of the elements such as MI and IK or MT and IK .areenergized by current flowing in opposite directions.

The relative directions of the currents along each of the sections MI,IK, M'I, and I'K' are indicated in Fig. 2A. An arrow ik indicates thedirection of the current energizing the section IK of the antenna shownin Fig. 2. Likewise arrows z'm, and im represent the direction of theenergizing current in sections IM, I'K, and I'M, respectively. Thesecurrents may be resolved into vertical and horizontal components. Thehorizontal current component in section IK is indicated by ikh, whilethe vertical polarized current component is represented by the arrowlabeled ilcv. Likewise, the horizontal current components in thesections IM, IK', and I'M are indicated by the arrows labeled imh, i'knand z"mh, respectively. The vertical current components in sections IM,IK, and IM are indicated by arrows labeled im ilcv and i'm'v,respectively. An examination or" the representation of the verticalcurrent components in the sections IK and IM reveals that, like thesystems shown in Fig. 1, the vertical current component in thesesections produce radiations which cancel in a plane normal to thedrawing. For the reasons stated in the description of the antenna systemshown in Fig. 1 the radiation due to the vertical current components inthe section IK and IM, taken alone, do not cancel in the direction FMK.In a like manner, the radiation due to the vertical current componentsin the sections IKand I'M, if considered alone, do not cancel in thedirection FMK. It is observed, however, that the radiation due to thevertical current components in the section IX and that in the section IKare directed in opposite directions. Likewise, the radiation due to thevertical polarized components in sections IM and I'M are in oppositedirections. The verticallypolarized component radiated by the sections1K and IM, together with those radiated by sections IK and I'M, not onlycancel in a horizontal plane to that of the drawing, but in additionsubstantially cancel in the direction FMK and FM'K. Accordingly, when azigzag element such as that shown in Fig. l and an oppositely bentelement are employed to form the system shown in Fig. 2, there is asubstantial reduction of the components of the undesired polarizationsover and above that produced by the system shown in Fig. 1. On the otherhand, the radiations from the horizontal current components of thesection IK, IM, IK and I'M are in the same direction, are additive inefiect and result in a radiated horizontally polarized signal of greaterintensity. The principle of radiation of the sections FG and GM and FGand G'M is similar to that of IK, IIvi, IK, and I'M. Since the principleof operation of the radiating member comprising the sections FG, GM, F'Gand G'M is the same as in the case of the radiating member comprisingthe sections IK, IM, IK and I'M, the combination of these sectionsoperates to effect not only a more intense signal of the desiredpolarization, but also to further reduce signals of undesiredpolarization. Similarly, an additional advantage is obtained byemploying a plurality of the elements shown in Fig. 2 arranged in acommon panel. For example, a panel may comprise two or more of theantenna systems shown in Fig. 2 placed in the same vertical plane andsupplied by a common radio frequency source.

Fig. 3 shows a modification of the system shown in Fig. '2. Two zigzagelements FGMIK and FGMI'K are supplied with radiating energy from a linel. 'The elements FGMIK and FG'MIK are the same as those shown in Fig. 2and the antenna system shown in Fig. 3 operates in a manner similar tothat shown in Fig. 2 to substantially eliminate the vertical polarizedwave component in all directions. Instead of connecting thenon-radiating elements between points F and K and F and K, thenon-radiating elements are connected between F and M, M and K, F and Mand M and K. The phasing of the antenna sections is as depicted by Figs.1A and 2. In order to secure the proper phasing, conductors FMK and FMKof the transmission line, the impedance of which is inherently low ascompared to that of each radiating section, are each made an evenmultiple of a half wave-length long for reasons pointed out inconnection with the description of Fig. 2. Each of the lines FM'K andF'MK' must also have, in order to insure the proper phasing, a lengthequal to twice an odd multiple of a half wave-length inasmuch as in thecase of each conductor the mid-point is connected to one of the zigzagantennas whereas the extremities are connected to the other zigzagantenna, and these antennas are associated with different terminals ofthe radio frequency source. Considered from another standpoint, theenergies arriving at M, for example, over the two paths FGM and FM forutilization by conductor MI agree in phase. Since the points orextremities F and F are oppositely phased and since the path FGM is awave-length long, the path FM must be made equivalent to an odd multipleof a half wave-length in order to secure the desired phase relation andcurrent distributions illustrated by Figs. 1A and 2. Consequently,conductor sections FM, F'M, MK and MK are each an odd multiple of a halfwave-length long. This type of construction of the antenna system isalso advantageous in that a series connection of all elements for sleetmelting currents may more readily be effected.

In Fig. 4, a perspective view of a complete unidirectional radiatingsystem embodying this invention is shown. The system comprises threepanels 5, i5, and 1 located in the same vertical plane. Each panel issimilar to the antenna shown in Fig. 2, except that. twelve instead ofeight radiating sections are employed. This construction necessitates areversal in the line connection in order to excite all radiatingsections with currents in the proper amplitude and phase. For example,the panel 5 comprises two radiating elements i3 and I4. Radio frequencycurrent is supplied to the radiating elements l3 and. M from a line itthrough two non-radiating transposed or reversed elements II and I 2.The non-radiating element ll connects the lower terminal of theradiating element i3 with the top terminal of the radiating element 14,while the non-radiating element i2 connects the lower terminal of theradiating element M with the top terminal of the radiating element IS.The transposed conductors ii and I2 are each an odd multiple of a halfwave-length long.

Three other panels 8, 9, and I 0 having the same configuration as panels5, 6, and 1 and having non-radiating elements the same as those ofpanels 5, 5, and I, lie in a vertical plane parallel to that containingpanels 5, 6, and 1, and are symmetrically located an odd number ofquarter wave-lengths to the rear of panels 5, 6, and 1, respectively.Both the front curtain of the system comprising panels 5, 6, and 'I andthe rear curtain comprising panels 8, 9, and H] are directly excitedinstead of permitting the rear curtain to obtain energy parasitically.The direct excitation of both curtains not only reduces the timerequired for tuning operations, but also greatly increases the accuracyof the adjustment for the null field to the rear of the system. A verydeep null to the rear of the antenna by directly exciting both curtainsin the proper phase relation is frequently obtained. The transmissionline for Supplying energy to the antenna system consists of a tie line263 connected to the line l6 between the center panels 6 and 9 of thefront and rear curtain. means of a feed line 22 and is supplied from thetie line to the panels 5, 5, 1, 8, 9 and ID by the line :6. The line 22is connected to a radio frequency Energy is supplied to the tie linebyquency source is represented in the drawing by a labeled blockdiagram. A source of low frequency current indicated by the labeledblock diagram is also connected to the line 22 by a line 29 through aquarter wave length line 25. Condensers 25 and 21 are connected acrossthe line 29, the condenser 21 being at a quarter wave-length distancefrom the source of low frequency current and the condenser 26. Thequarter wave-length line 25 together with the condensers 26 and 21 forman anti-resonant current at the frequency of the energy supplied by theradio frequency source. The condensers 24 are low frequency blockingcondensers which prevent energy from the low frequency source fromentering the high frequency source; In a manner described in U. S.2,098,266, granted to E. J. Sterba on July 16, 1935, the antenna systemis supplied with the low frequency current for sleet melting and thehigh frequency current for radio transmission.

Experiments have demonstrated that the tie line 29 should preferably bean odd number of quarter wave-lengths long. The tie line 20 is connectedstraight across without crossing if it is 1%, etc., wave-lengths longand is crossed degrees phase reversal) if it is 1%, 2%, etc.,wavelengths long. The feed line 22 is tapped across the tie line 20 at apoint approximately A 1%, etc., wave-lengths from the rear curtain. Thebest position is critical to within a few inches and depends to acertain extent upon the accuracy of the tie line length. It has beenfound that if the tie line length is either increased or decreased asmuch as an eighth wave-length from the optimum odd quarter value, therequired position of the feed tap is found to move on the tie line byapproximately an equal distance.

From the standpont of the suppression of signals of undesiredpolarization and the reinforcement of signals of the desiredpolarization, the principle of operation of the system shown in Fig. 4is similar to that shown in Fig. 2. However, by properly selecting thephase and amplitude of the radiating currents in the two curtains, aunidirectional radiating characteristic is obtained.

The standing wave loops on the half wavelength elements of each zigzagantenna in the systems of Figs. 2, 3 and 4 are considerably larger inamplitude and produce greater radiated components than those establishedon the half wavelength elements of the prior art system illustrated byFg. 1, since the extremities of each zigzag element and also themid-points of the elements in the system illustrated by Fig. 3 aredirectly connected to the transmission line whereby the traveling wavesfrom the source follow diverse or relatively short paths, undergominimum attenuaticn and initiate strong standing waves at the apex ormid-point of the radiating structure.

- The system of Fig. 4 is also arranged for simultaneous energ zationwith sleet melting and radio frequency current. Referring to Fig. 4,blocking condensers l 4 which are capable of passing high or radiofrequency currents but which eifectively block the low frequency ordirect currents employed for sleet melting, are associated with thearray of each panel, the tie line 20 and the transmission line I6. Awave impedance 2| is also connected to the two elements of each paneland to the line H. Each wave impedance 2| is of the conductive type andcomprises two parallel conductors, preferably consisting of coppertubing, an odd multiple of quarter wave-length long source through twocondensers 24. The radio freand short-circuited at the far end by meansof a 75 solid. metallic bar or other conductor. Each of these impedancesofiers substantially infinite impedance to waves of a particularfrequency. In a manner similar to the system described in the abovestated patent of applicant, the condensers and impedances are arrangedin the system so the panels are connected in series for sleet meltingcurrent, while the panels are in parallel for the radio frequency wavepropagation.

5 shows the ratio of the horizontally polarized components in ahorizontal plane along the earth radiated by the system shown in Fig. 4and that radiated by a single half wave-length antenna which is placedat the mean height of the directional antenna. The solid curve is thetheoretically calculated result, while the points are the-actualexperimental observations. The data from which the points were plottedinclude only the angular range extending between the two nulls on twosides of the principal lobe. Examination of Fig. 5 reveals that forequal power supplied to the simple horizontal antenna and to the arrayof Fig. 4 there are 19 decibels improvement in a horizontal direction. a

While preferred embodiments in this invention have been illustrated anddescribed, various modincations therein may be made without departingfrom the scope of the appended claims.

What is claimed is:

An antenna system comprising a plurality of pairs of z gzag, verticallyarranged radiating elements comprising a plurality of sections, thelength of a section of each element being approxi- ,,-.iately one-halfwave-length, the corresponding angles of each of said element of saidpair being oppositely bent from the other element of the pair and theapices of the corresponding angle of the elements of each pair being inthe same horizontal plane, a second plurality of pairs of radiatingelements substantially identical with said first plurality of verticallyarranged zigzag elements means for exciting directly said plurality ofelements and said second plurality of elements comprising a connectionbetween a source of energy and each extremity of each zigzag element.

2. An antenna system comprising a front curtain comprising three panelsarranged vertically,

panel comprising a radiating element reversely bent at approximatelyeach half wavesely bent, a rear curtain substantially identical withsaid front curtain, a source of radio frequency current andnon-radiating means for supplying current from said source directly toeach extremity'of each element included in said front and rear curtains.

3. A radiating system comprising a first V- shaped vertically arrangedradiating member, approximately one-half wave-length on a side, a secondV shaped radiating member, approximately one-half wave-length on a sidearranged in the same vertical plane as said first member, the opening ofsaid first member facingthe openof said second member, a source of radiofrequency current and means for supplying from both terminals of saidsource in-phase currents to the extremities of each member, the currentssupplied to the terminals of one member being in opposite phase withrespect to the currents supplied to the other member, whereby the membersides extending inparallel directions are energized in phase and only ahorizontally polarized field is effectively radiated.

Aradiating system comprising a first stack of V-shaped radiatingmembers, approximately one-half wave-length on a side, seriallyconnected to each other and arranged in the same vertical plane, asecond set of V-sha-ped stacks, approximately one-half a wave-length ona side, serially connected to each other, arranged in the same verticalplane as said first stack, said V-shaped members of said second stackfacing the correwave-length long, each of the sections of each of radiofrequency waves and a transmission line for supplying from differentterminals of said source in-phase radio frequency waves to theextremities of each-stack and oppositely phased Waves to said firstandsaid second stacks whereby substantially strong standing waves areestablished on each half wave-length element and only horizontallypolarized wave components are radiated.

5. A radiating system comprising three radiating panels, arranged in thesame vertical plane, each of said panels comprising two zigzag elementshaving sections approximately one-half a wavelength long, each of thesections of each of said elements being symmetrical with but oppositelybent from adjacent sections of said element, a source of waves andnon-radiating means for supplying waves from said source to a pluralityof points in each of said panels.

6. In a radio system, an antenna comprising a plurality of seriallyconnected half wave-length radiating sections arranged to form a zigzagelement, a source of radio frequency energy, a countel-poise and meansfor supplying in-phase energy to the. extremities of said antenna andenergy oppositely phased to said first-mentioned energy to saidcounterpoise.

'7. A system in accordance with claim 6, said counterpoise comprising aplurality of half wavelength radiating sections arranged to form azigzag element, said means comprising a pair of connections extendingfrom the opposite terminals of said source to said extremities and asimilar pair of connections extending to the extremities of saidcounterpoise, and a low frequency source connected in series with saidantenna and counterpoise.

8. In a radio system, a pair of antennas, the corresponding terminals ofwhich are more closely positioned than the terminals of either antenna,and means for simultaneously energizing said antennas with radiofrequency current and sleetmelting current, said means comprising asleetnielting current source, a radio frequency source, and a line forconnecting said sources to each antenna, a first terminal of the firstantenna being connected through a low frequency impedance to one lineconductor and the corresponding first terminal of the second antennabeing connected through a similar impedance to the other line conductor,the second terminal of the first antenna being connected through a pathof substantially zero impedance to the second-mentioned line conductcrand the corresponding second terminal of the second antenna beingconnected through a similar path to the first-mentioned conductor, and apath of substantially zero impedance for the sleet melting currentconnecting the corresponding first terminals of said antennas.

9. In a radio system, an antenna, a counterpoise, a translationdeviceconnected to one'set of corresponding points on said antenna andcoun- ,erpoise, a transmission line connecting said points -to a secondset of corresponding points on said antenna and counterpoiseelectrically separated from the first set by at least two wave-lengths,the conductors of said line being positioned relatively close together,and said line being shorter electrically than each of the antenna andcounterpoise portions included between said two sets of points andhaving a relatively low impedance, whereby substantially no radiationoccurs from said line and a maximum amount of energy is delivered tosaid second set of points.

10. In combination, a zigzag antenna element having a pair of terminalsand a length equal to a plurality of wave-lengths, a zigzag counterpoiseelement having the same length and a pair of terminals, a transmitterconnected between one set of corresponding antenna and counterpoiseterminals, a line connecting said set of terminals and the remaining setof corresponding terminals, the conductors of said line being positionedrelatively close together and each having an electrical length less thanthat of the antenna or the counterpoise and equal to a multiple of ahalf wavelength, and said line having a relatively low impedance,whereby substantially no radiation occurs from said line and a maximumamount of energy is delivered to said remaining set of ter- 10 minals.

ERNEST J. STERBA.

